The present invention relates generally to catalyst systems, polyisocyanurate/polyurethane (PIR/PUR) foam formulations, and methods of making PIR/PUR foams.
Typically, polyisocyanurate/polyurethane (PIR/PUR) foams are made by reacting a polyol and a polyisocyanate in the presence of a catalyst. Additional additives can be present. PIR/PUR foam products have excellent thermal stability and flame resistance. Isocyanurates retain their strength to temperatures of about 160° C. and are resistant to most organic solvents, acids, alkali, ultraviolet light, and humidity.
Certain carboxylate salts, such as, for example, certain alkali metal carboxylate salts, have been used as catalysts in the production of PIR/PUR foams. The use of commercially available alkali metal carboxylate salt catalysts, however, often leads to undesirable foam processing problems which are particularly significant in continuous foam operations. A distinctive “step” is observed, which is normally associated with the onset of the trimerization process, when measuring the rise speed profile of the foam, or by plotting the foam height versus time. This trimerization “step” causes a significant change in the speed of the foam rise; in essence, the foam expands at two different rates during the foaming process. In a continuous polyisocyanurate/polyurethane foam lamination operation, it is difficult to adjust the speed of the production unit to match the change in the speed of the foam rise. The result can be foam overpacking or foam back flow. This undesirable rapid rise in foam height is particularly troublesome when processing polyisocyanurate/polyurethane formulations at a high Isocyanate Index. That is, the change in the rate of foam rise is much more dramatic at a higher Isocyanate Index. Consequently, it is a technical challenge to produce desirable low flammability foam products, with a high isocyanate index, when using conventional alkali metal carboxylate salt catalysts.
As compared to alkali metal carboxylate salt catalysts, commercially available polyisocyanurate trimerization catalysts based on hydroxyalkylammonium carboxylate salts show different processability in continuous operations. They provide a smoother rate of rise profile and have a less significant trimerization “step.” That is, the rate of foam rise is more consistent, even at a higher Isocyanate Index. However, hydroxyalkylammonium carboxylate salt catalysts often can be unstable at temperatures above about 100° C., decomposing into volatile amine by-products. This decomposition process causes the release of volatile amines and can impart an undesirable amine odor to finished foam products. The polymerization reactions that produce PIR/PUR foam are highly exothermic, often leading to foam processing temperatures in excess of 100° C. Hence, hydroxyalkylammonium carboxylate salt catalysts can provide more predictable foam processability, but sometimes at the expense of a foam product with an undesirable amine odor.
Thus, there exists a need for a catalyst composition that can offer a smooth rise profile—foam height versus time—for producing PIR/PUR foams in continuous operations. Further, the catalyst composition also should perform well in foam formulations with a high Isocyanate Index. At the same time, the catalyst composition should provide equivalent or faster surface cure when compared to commercially available catalyst systems, such that the foam products made with the catalyst composition can have reduced surface friability and enhanced surface adherence during the manufacture of finished products such as laminated foam panels. Optionally, depending upon the selection of the catalyst components, the catalyst composition can be thermally stable at the temperatures which PIR/PUR foams normally encounter during manufacturing, and produce foams that are substantially free of volatile amines and/or amine odors.